Thpo tanned leather



The invention described herein may be manufactured and used by and for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to the tanning of animal hides in the manufacture of leather and more particularly to the process and the product which are described herein.

As a background for imparting a clear understanding of the invention as claimed, representative publications in the field here concerned are The Chemistry and Technology of Leather, volume l-Preparation for Tannage, edited by Fred OFlaherty et al., and published in 1956 by the Reinhold Publishing Corporation, New York, New York; Modern Practice in Leather Manufacture, by John A. Wilson, and published in 1941 by the Reinhold Publishing Corporation; and The Condensed Chemical Dictionary, by Arthur Rose, published in 1956 by the Reinhold Publishing Corporation. These texts may be taken as references, definition sources and the like, for the material herein.

The major portion of the leather which is presently produced commercially is tanned by processes which use chromium salts or vegetable tannins. The leathers which are tanned by processes using chromium salts may vary in color from a light blue to a blue green. The leathers leather which is white throughout its structure. Both the bleaching processand the pigmentation process require additional processing and hence additionalexpenses or added costs to the manufactured product.

Patent Number 2,732,278, issuedon January 24, 1956, to Edward M. Filachione, discloses a tannage which yields a leather with no discoloration by treating hides with the chemical tetrakis (hydroxymethyl) phosphonium chloride which is referred to herein as THPC and to which compound the texts give the empirical formula (HCH PCl.

In experimental research on the processes so disclosed it has been found that the finished white leather produced by the Filachione process gives ofii an objectionable odor, which may be due to the presence of phosphine (PH or the like, liberated from the tanning agent, It

ted Sttes Patent 0 ments of the objects of the invention commensurate and consistent with the invention as claimed and also setting out the exact nature, the operation and the essence of the invention complete with proportions and techniques that are necessary with its use. The purpose of the invention also is stipulated. The presentation is adequate for any person who is skilled in the art and science to which thew invention pertains to use it without involving extensive experimentation. The best mode of carrying out the invention is presented by the citing of specific operative examples inclusive of the preparation and the use of at least one example of the invention.

This invention concerns the tanning of animal hides in the manufacture of leather by the use of tetrakis (hydroxymethyl) phosphonium chloride or THPC or (HOCH PCI, with various organic compounds of trivalent nitrogen in the tanning process. In amount, one or two moles and preferably two moles, of the organic compound of trivalent nitrogen are added to each mole of the THPC. The trivalent nitrogen compound may have been methylated or methylolated in the same molar ratios, if desired. The reaction ranges in proportions, temperatures and pressures are as set forth herein, with standard temperatures and pressures understood where so implied.

The animal skins worked on are the raw stock product of the beam house processes, trimmed, fleshed, unhaired, bated and scudded to produce the true skin or the corium. The corium is an interwoven network of fiber bundles of the fibrous protein collagen which reacts with tanning agents in skin processing. Collagen or collogen is a composition of amino acids of which twenty-one are identified as being derivatives of by R substitutions. In common witho'ther proteins,

collagen is composed of alpha amino acid molecules oxidized to convert it into tris (hydroxymethyl) phosphine may be that free hydroxymethyl groups are oxidized by the tanning reagents used or by the air to liberate phosphine. The avoidance of this reaction is one of the objects of this invention. Providing leather of an unobjectionable odor and white throughout its structure are other objects of this invention. Another object of the present invention is the provision of a new and an improved leather which has good heat stability. The proc- 'ess described herein employs nonstrategic materials.

A brief summary of the invention follows, indicating its nature and substance together with the above state- 7 oxide or THPO, in neutral or in basic solutions. It is theorized that this THPO is the tanning agent in alkaline solutions and further that both THPC and THPO tan hides by condensing with the free amino or amido groups of the hide somewhat in the following manner.

Collagen amino group-THPO:

A similar reaction is believed to occur between the collagen amino group and THPO with the exception that in this latter reaction, two hydroxymethyl groups are unreacted and are believed to react with tanning reagents or with limited quantities of air to liberate from the leather in the Filachione process previously referred to Patented July 25, 19 61,-

phosphine or other odorous vapor, which objectionable odor is avoided in the process disclosed herein.

The elimination of potential sites for the oxidation of THPC has been accomplished by reacting THPC with various trivalent nitrogen compounds, such as the examples given in the following reactions, and the like.

Reactions (1A) THPC:

(HOCEQMP Ol+2CHr( CH NHz n-amylamine H [CHgN-(CH;) iCHsh 2B) Collagen amino group:

Reaction product of 2A above Reaction product of 3A above It will be apparent from the above tanning reactions that free hydroxymethyl groups (CH OH) attached directly to the phosphorus atom have been eliminated from the reaction product and consequently the occurrence of phosphine PI-I in the leather end product has been eliminated. A selection of the hydrocarbon chain attached to the trivalent nitrogen permits control over the desirable properties imparted to the leather end product. Both primary and secondary amines and amides can be used in this application.

The above examples illustrate the applicability of the reactions disclosed herein and are not to be construed as limiting the reaction to these specific organic com-' pounds of trivalent nitrogen.

Specific laboratory procedures illustrating the preparation of the tanning agents disclosed herein in laboratory quantities and under laboratory conditions of temperature and pressure are the following tanning preparations.

Tanning preparations (1C) 2.0 grams or 0.01 mole of THPC are weighed out and are preferably mixed in a glass container with 1.7 grams or 0.02 mole of n-amylamine. The iso amyl amines can be substituted for the normal amyl amines where desired. The resulting reaction is exothermic and heating is continued on a hot plate to the completion of the reaction set forth in IA above. The reaction temperature is adequate if a boiling temperature is maintained. The resulting solution is applied to beam processed hides as described in the Filachione patent and in the cited texts.

(2C) 2.0 grams, or 0.01 mole of THPC are weighed and are mixed in a beaker or the like with 2.1 grams or 0.02 mol of diethanolamine. The reaction is exothermic. The solution is heated at boiling on a hot plate or the like until the reaction is completed. The product is poured into 50 milliliters of water and is found to have a pH of 7.0. Sufiicient acid such as hydrochloric acid is added to the solution to adjust the solution pH to 2. The resultant solution is then ready for its use in the tanning of hides into leather.

(BC) 2.0 grams, or 0.01 mole of THPC are weighed and are mixed in a beaker or the like with 2.5 grams or 0.02 mole of melamine and with 50 milliliters of water. The mixture is adjusted to a pH of 2 by the addition of hydrochloric acid or the like, and heat is applied. At 70 C. the solution is clear. Heating of the solution is continued until a solution temperature of C. is reached at which temperature the pH of the solution is increased to 7.0 by the addition of triethanolamine. This pH terminates the reactions involved and prevents the formation of insoluble products. The solution so made is then used in the tanning of hides in the manufacture of leathers.

. The use of the above solutions in the process of ten ning hides in the manufacture of leather may be illustrated by the following procedures, wherein the abbreviation Ts stands for the shrinkage temperature of the hide or or the leather, as determined in a hot water bath and as commonly used in the literature concerning tanning methods.

The hides in these illustrative procedures are cowhides which had been given the usual commercial beamhouse operations of unhairing, bating and pickling after which they had been stored in a deep freezer. In the experimental work through which this invention is reduced to practice, the tanning is done in small glass jars which fit into suitable laboratory agitation equipment, of which the commercially available Launder-Ometer may be taken as being illustrative. It will be apparent that larger apparatus and correspondingly larger proportions of reactants will be used in the practice of the processes disclosed herein on full size hides ina commercially operated installation. The turning of the Launder-Ometer provides agitation. Tanning is accomplished at room temperatures of about 23 C. to 30 C. The percent of tanning compounds which are used are based on 40 percent of the Weight of the drained, pickled weight of the stock, which is rawhide and which has a pH of about 3.

Tanning examples (1D) In this example cowhide stock weighing 9 grams is treated with 0.9 gram of the above preparation 1C solution, which is a viscuous liquid. 50 milliliters of water, with 0.9 gram of NaCl dissolved in it, which weight of NaCl is about 10% of the weight of the cowhide stock, are added to the reactants and to the hide in a glass jar. If preferred, the tanning compound may be dissolved in the water and the NaCl added and dissolved in the water solution of the tanning compound.

The jar is placed in an agitating device, such as the Launder-Ometer mentioned, or the like. The agitating device is operated for illustratively about forty minutes. The solution applied to the hide at this point is at a pH of 6.0 and the hide has a shrinkage temperature or Ts of 48 C. The container or jar is then opened and a dilute solution of sodium carbonate or the like is added to the solution until the solution has a pH of 7.0. The container is then closed and the Launder-Orneter or agitator is run for about one hour.

The container is again opened and the solution is found to have a pH of 6.0 and the hide is found to have a shrinkage temperature or Ts of 83 C. The pH of the solution is then increased to 9.0 by the addition of some of the sodium carbonate solution and the container is closed and is returned to the agitator where it is again agitated for another thirty minutes. At the end of this period of agitation the pH is found to be 7.0 and the stock or hide is left setting in the solution overnight. In the morning the pH is found to have remained at 7.0 and the Ts has risen to 86 C. The tanned leather is then washed and dried.

The resultant tanned leather is found to be white throughout its structure, to have no objectionable odor, and to have good heat stability.

(2D) In this example a pickled cowhide stock weighing 10 grams is treated with 110% of its weight or 1.0 gram of the above preparation 2C solution in 1.3 milliliters of water and 1.0 gram of NaCl, which again is 10% of the stock weight.

The 1.0 gram of the tanning compound solution 2C, the 1.0 gram of NaOl and the 13 ml. of water are combined in a jar that illustratively is made of glass. After the salt is dissolved, the 10 grams of dry pickled cowhide stock is added to the resultant solution which at this stage is found to have a pH of 2.0.

The jar is placed in the Launder-Ometer and is agitated for 30 minutes at which time the solution within the jar has a pH of 2.0 and the leather has a Ts of 51 C. Agitation of the jar and of its contents is then continued for about 2 /2 hours at which time the solution pH is 3 .0 and the leather has a Ts of 49 C. The solution pH is adjusted to 6.0 by the addition of dilute sodium carbonate and the agitation of the jar is continued for 1 /2 hours at which time the solution pH is 6.0 and the Ts is 60 C. The solution pH is then raised to 7.0 by the addition of dilute sodium carbonate and the leather is is 5.0 and the Ts is 81 C. The pH is'then increased to 9.0 by the addition of dilute sodium carbonate and the jar with its contents is agitated for 1% hours. The pH at the completion of this run is 6.0 and the Ts is 85 C. The leather is removed from the jar, washed with water and dried at room temperature. The leather so produced is white throughout, and has no objection able odor.

(3D) In this example a pickled cowhide stock that weighs 13.6 grams is to be tanned. 10% of the weight of the cowhide stock, or 1.4 grams of the above defined tanning solution 3C in 15 milliliters of water is added to a jar. The pH of the solution at this stage of the process is 2.0. The addition to the jar of 1.4 grams of NaCl causes a precipitate to form .50 milliliters of water added to the jar places the precipitate in solution.

The pickled cowhide stock weighing 13.6 grams is then added to the solution in the jar. The jar is placed in the Launder-Ometer and is agitated for 30 minutes. The pH of the solution is then taken and is found to be 2.0. The Ts is found to be 41 C. The jar and its contents are then agitated for 2V2 hours. The pH is then 2.0 and the Ts is 42 C.

The pH is adjusted to 6.0 by the addition to the jar of dilute sodium carbonate and the agitation is continued for 1 /2 hours. The pH is then found to be 4.0 and the Ts is 49 C. The pH is adjusted to 8.0 by the addition to the solution of dilute sodium carbonate and the hide is allowed to remain in the solution overnight. The next morning the pH is found to be 5.0 and the Ts is 72 C. The pH is then adjusted by the addition of dilute sodium carbonate to 9.0 and the jar is agitated for 1% hours. The pH is then 6.0 and the Ts is 76 C. The leather is then removed from the jar and it is washed and air dried at room temperature and pressure. The leather is odorless and it is White throughout.

(4D) In this example vegetable tanned leather is retanned by one of the tanning preparations disclosed herein. A sample of vegetable tanned leather weighing 24.6 grams is placed in a jar and is wet back with Water. A tanning compound is made by adding 24.6 grams of a 10% tannin solution to 2 grams or 0.01 mole of THPC and 2.1 grams or 0.02 mole of diethanolamine in 50 milliliters of water. The tanning compound is added to the hide in the jar. The initial Ts of the hide is 77 C. and after the hide has stood in the tanning compound for 12 hours the Ts of the hide is found to be 80 C. The vegetable tanned leather so retanned is then Washed and dried. This leather retained the brown vegetable color imparted to it by the vegetable tanning process by which it was produced.

The embodiments of the invention that are disclosed herein are in the nature of actual experimental reductions to practice of the invention from which have evolved expressed conceptions and theories of its operation. It is to be understood that the invention may be practiced beyond the precise details that are disclosed herein and that the invention covers variations and modifications within the scope of the appended claims.

I claim:

1. Leather comprising collagen with its amino group of the structure:

out

7 8 2. Leather comprising collagen with its. amino group- 3. Leather comprising collagen with its amino group. of the structure: of. the structure:

v HNH 5011 ar H N e H \H H H H 4 0-0 011 O N- )P==O H H HNH H H H H OH References Cited in the file of this patent g H 10 UNITED STATES PATENTS H \H H 2,309,188 Girim et a1. Ian. 26, 1943 g-g 2,668,096 Reeves et al. Feb. 2, 1954 2,732,278 Filachione Ian. 24, 1956 

1. LEATHER COMPRISING COLLAGEN WITH ITS AMINO GROUP OF THE STRUCTURE: 